The relevant prior art discloses the catalytic conversion of glycerol to alcohols by means of a catalytic thermochemical process without the need for an external supply of hydrogen. D'Hondt et al, Chem. Commun., 6011-6012 (2008), discloses the catalytic conversion of glycerol to propylene glycol in the absence of added hydrogen utilizing a platinum impregnated sodium/yttrium (NaY) zeolite catalyst. Utilizing this system, D'Hondt obtained a glycerol conversion rate of 85.4% and a yield of propylene glycol of 64% in 15 hours. The conversion rate and yield were reduced to 58.8% and 41.5%, respectively, if the reaction was run for only 4 hours. If the reaction was run for only 1 hour, the conversion rate and yield were reduced to only 18.1% and 25.0%, respectively.
Gandarias, Applied Catalysis B: Environmental, 97:248-256 (2010) likewise discloses the utilization of a platinum catalyst. The platinum catalyst of Gandarias was supported on an amorphous silica/alumina. Gandarias disclosed that, when exogenous hydrogen was added to the system, after a reaction time of 24 hours and at a pressure of 45 bar, a conversion rate of glycerol of about 20% was obtained with a yield of propylene glycol of about 32% (if the reaction was performed at 493° K) and a conversion rate of 90% with a yield of about 11.2% (if the reaction was performed at 513° K). However, in the absence of hydrogen, the conversion rate of glycerol after 24 hours was only 22.7% at 493° K and 34.8% at 513° K, and the yield of propylene glycol was 35.3% and 6.8%, respectively.
Roy, Catalysis Today, 156:31-37 (2010), discloses the catalytic conversion of a glycerol feedstock utilizing a reaction time of 6 hours and a catalyst made of an admixture of platinum and ruthenium. Conversion of glycerol at 493° K was reported to be about 50% with about 47% selectivity for propylene glycol. Conversion at 513° K was reported to be about 66%, but selectivity for propylene glycol was only about 30% at this higher temperature.
Similar results were disclosed in Chaudhari, U.S. Patent Application No. 2011/0004029. Utilizing either a platinum catalyst, a ruthenium catalyst, or a catalyst containing both platinum and ruthenium, glycerol was converted to various alcohols. As reported in Chaudhari, the conversion of glycerol by hydrogenolysis in the absence of external hydrogen with a 6-hour reaction time occurred with a temperature dependent conversion efficiency between 20.6% and 82.6%. At 473° K, conversion efficiency was 20.6% and selectivity for propylene glycol was 53.1%. However, as temperature was increased the conversion efficiency increased, to 82.6% at 523° K, but the selectivity of propylene glycol at this higher temperature was reduced to only 26.5%.
Smith, J. Phys. Chem., 59(9):820-822 (1955), discloses that a limited amount of hydrogen is associated with Raney nickel catalysts. Approximately one-half to one atom of hydrogen is present per atom of nickel in the catalyst. Smith discloses that, during a catalytic reaction, the hydrogen from the catalyst is removed and the activity of the catalyst is lost. Smith further discloses that the hydrogen lost during reaction is difficult to replace and that the activity of the Raney nickel catalyst therefore is reduced during a reaction as the hydrogen is removed from the catalyst.
Perosa, Ind. Eng. Chem. Res., 44:8535-8537 (2005), discloses the selective hydrogenolysis of glycerol to alcohols using a Raney® nickel (W.R. Grace & Co., Columbia, Md.) catalyst. Perosa discloses that a conversion rate of 12% with 93% selectivity was obtained after 20 hours with the addition of 10 atm of exogenous hydrogen gas. Perosa discloses that pressures of hydrogen below this level were insufficient to achieve significant conversion.
Each of the above cited references is incorporated herein by reference in their entirety.
Significant disadvantages are present with the above prior art methods for conversion of glycerol to alcohols. Most significant is that the reaction time required for the conversion of glycerol to alcohols, as disclosed in the prior art, is too long for the methods to be economically viable. A conversion of glycerol in a much shorter time span, such as two hours or less, would be desirable. Additionally, the conversion efficiency of glycerol and the selectivity for propylene glycol are low in the methods of the prior art. Therefore, it would be advantageous for a method to either increase the efficiency of glycerol or acetol conversion above that disclosed in the prior art or to increase the selectivity of this conversion to produce propylene glycol. It would further be advantageous for a method to both increase the efficiency of glycerol or acetol conversion and increase the selectivity of this conversion to propylene glycol.